Biomass Feedstocks

Opportunities to increase biofuels This feature on biomass feedstocks is the first in a series of four examining biomass energy.

With increasing concerns over dwindling reserves and unstable supplies of petroleum coupled with climate change caused by the burning of fossil fuels, the search is on for cleaner energy. Biomass is a solar energy resource with the potential to be a significant contributor to the United States’ energy portfolio with a low carbon footprint. Several types of biomass are currently used as feedstocks in energy conversion processes to produce liquid fuels, power, and heat, including wood, agricultural, and forest product residues and municipal solid and industrial waste.

Energy goals set by President George W. Bush (Twenty in Ten), the U.S. Department of Energy (30×30), the private sector and interest groups (25x’25), and Congress (which recently enacted Energy Independence and security Act of 2007) to develop biobased fuels will require an unprecedented engagement of American agriculture in domestic energy production.

Many states are also supporting biofuels. For example, California recently enacted a Low-Carbon Fuel Standard to reduce the carbon intensity of transportation fuels sold in that state by 10 percent by 2020. Many of the low carbon fuels expected to be commercially available in large quantities in California within the 2020 time horizon are anticipated to be biofuels.

Research and development the focus

The primary biofuels produced at a commercial scale today in the United States are ethanol, which exploits the starch resources in corn and other grains, and transesterified biodiesel from oilseed crops, such as soybeans and animal fats. Ethanol production and use is approaching 3 percent of our total national fuel consumption today and is expected to reach about 7 percent by the end of this decade. However, to expand anticipated biofuels production in the future and as new biomass energy conversion processes are perfected to produce “advanced” biofuels, research is focusing on improving the characteristics of existing biomass feedstocks as well as exploring the potential for new energy crops and new biobased fuels/ products.

For example, research is being conducted on sugar and starch crops to make them more efficient in existing conversion processes, e.g., new strains of sugarcane that produce more sugar and enable these tropical crops to be grown in more temperate climates and oilseed crops that increase the yield of oil and have enhanced fuel quality attributes.

Most of the federal research and development effort is focused on developing the “next generation” of biofuels that will allow lignocellulosic crops, both herbaceous and woody plants, and crop and forestry residues to be converted into biofuels. Both herbaceous and woody crops are more widely available biofuel feedstocks than sugar and starch crops. One of their greatest advantages is that they are short-rotation, perennial crops; they regrow after each harvest, allowing multiple harvests without having to be replanted. Switch grass, which is indigenous to U.S. prairies where it is grown to reduce soil erosion and to create wildlife habitats, is being studied extensively for its potential as an energy crop. One recent study, conducted by the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) shows that switch grass yields more than five times the energy needed to grow, harvest, and transport the grass and convert it to ethanol. Alfalfa is also another potential energy crop that, unlike corn and other grasses, fixes its own nitrogen and thus requires less fertilizer.

Crop and forestry residues may also be collected as by-products, such as corn stover or rice or wheat straw, or they may be collected at processing facilities such as lumber mills, cotton gins, or vegetable processors. Residues, especially corn stover, are expected to be the first feedstocks for cellulosic biofuels to be used. However, excessive residue removal can increase soil erosion and reduce soil productivity. ARS recently conducted a longterm study in eastern Nebraska to evaluate the impact of stover harvested for bioenergy on soil productivity. It concluded that more residues than previously thought must be retained on the field to avoid adverse impacts on soil productivity. Major breakthroughs in cellulosic conversion and commercialization are expected within the next five to ten years that will help to bring additional sources of cellulose into sustainable, environmentally sound use.

Traditional oilseed crops, including soybeans, canola, mustard seeds, and sunflower seeds, are grown throughout the United States for biodiesel production and new crops, such as camelina and jatropha, show potential. Some varieties of algae are known to produce large amounts of fatty acids and have been proposed as biofuel feedstocks.

The future’s best of the best

The best energy crops may be those that are multipurpose and allow farmers to respond to market changes by combining food, feed, fiber, and biofuel product streams. Many advances have already been made with conventional plant breeding using molecular genetics and plant physiology to significantly improve crops. These technologies can also lead to significant improvements in bioenergy feedstocks.

In the future, engineered plants may be the solution to low- cost, abundant feedstocks. By tweaking plant genes, scientists can encourage production of more biomass or change a plant’s cell wall composition so that it can be readily converted into biofuels or industrial products such as lubricants, inks, fabrics, or glue. ARS has 20 gene banks across the country that can be used to design, develop, and produce better energy crops.

Considerations vis-a-vis sustainability will be an important consideration in the emerging, high-volume biofuels industry. A federal government National Biofuels Action Plan points out that there is currently “limited understanding of potential impacts of large-scale energy feedstock production on land uses, water, carbon sequestration, and ecosystems (particularly excess fertilizers, pesticides, and sediment in surface waters) … “

Because of the wide variation in biomass feedstocks and their impacts by geographic location, research is being conducted on many of these issues on a regional basis. Land grant and other universities, as well as ARS, are evaluating various crops for suitability and sustainability based on eco-region, genetic variation, and production economics. Some land grant universities have joined together in five geographical locations throughout the country to address regional biomass feedstock capabilities in terms of sustainable production for energy purposes. Many of these crops will be on public display at the USDA Energy Garden exhibit being developed for mid-2008, (see USDA Candidate Plants on previous page) to inform the public on a range of plants that are grown in the United States that are, or have potential to be, used as renewable energy sources.

The biomass resources in this country have the potential to make a significant impact on energy use not only as fuel but as bioproducts. For this potential to come to fruition, it will require the research, education, and extension resources of USDA and its university partners to help develop the technology, sustainability, and profitability that will be needed to build a clean and prosperous energy future.

Gale A. Buchanan is Under Secretary for Research, Education, and Economics, USDA, Washington, D.C., USA; Gale.Buchanan@usda.gov. Joseph A. Dunn is a special advisor to the Under Secretary for Research, Education, and Economics, USDA; Joseph.Dunn@usda.gov. ASABE member James R. Fischer is a scientific advisor for Energy, Science, and Education to the Under Secretary for Research, Education, and Economics, USDA; James.Fischer2@usda.gov. Stanley R. Johnson is distinguished professor emeritus, Iowa State University, Ames, and assistant to the dean, University of Nevada, Reno, USA; sjohnson@cabnr.unr.edu. Research assistance was provided by Janine A. Finnell, Technology & Management Services, Inc., Washington, D.C., USA; jafinnell@ yahoo.com.